High density, high stability, sized metal oxide powder and process for making same

ABSTRACT

The present invention relates generally to a novel approach to treating spent pickling acids, and a useful product resulting from such treatment or recycling approach. More specifically, the present invention is directed to compositions of matter of a high density, high stability, high absorption capacity composite metal oxide preferably comprising designed ratios of iron oxide and zinc oxide from inexpensive, waste raw materials such as, spent hydrochloric galvanizing pickling acids. Further, the present invention describes a process for reacting the spent pickling acids with an alkali hydroxide, oxide or carbonate to generate an alkali chloride and a mixture comprising iron and zinc oxides and hydroxides. The product of the reaction is then filtered, and the content of the alkali in the solids is adjusted according to application requirements, after which the solids are calcined and then screened to a required particle size. One beneficial application of the composite metal oxide of the present invention is its use as a drilling fluid weighting agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to a novel approach to treating spent pickling acids, and a useful product resulting from such treatment approach. More specifically, the present invention is directed to compositions of matter of a high density, high stability, high absorption capacity composite metal oxide preferably comprising designed ratios of iron oxide and zinc oxide from inexpensive, waste raw materials such as, spent hydrochloric galvanizing pickling acids. Further, the present invention describes a process for reacting the spent pickling acids with an alkali hydroxide, oxide or carbonate to generate an alkali chloride and a mixture comprising iron and zinc oxides and hydroxides. The product of the reaction is then filtered, and the content of the alkali in the solids is adjusted according to application requirements, after which the solids are calcined and then screened to a required particle size.

The steel and metalworking industry uses hydrochloric acid (HCI) for “pickling” metal parts to remove rust and shavings and to prepare the surfaces for further treatment such as galvanizing, plating or painting. Spent pickling liquor normally contains iron (Fe) as well as other heavy metals present in the steel alloy. In the galvanizing industry, for example, the pickling acid solution is also used to reprocess parts with failed galvanizing and plating, thus resulting in potentially high zinc (Zn) content It is a practice in the galvanizing industry to separate the pickling acids used primarily for stripping the failed galvanized coating from those used for removing the outer layer of rust from metal parts prior to galvanizing and completing the stripping of remaining galvanizing layer. Thus, the industry produces two typical concentrations of zinc in the spent pickling acid. A majority of the spent pickling acid from galvanizers contains primarily iron chloride with lower amounts of zinc chloride. Depending on the types and volume of business experienced by a particular galvanizing shop, a minority of the spent pickling acid contains primarily zinc chloride and a lower amount of iron chloride. In addition, it is a practice problematic for downstream disposition of the galvanizing spent pickling acid that the galvanizers add lead or bismuth to the zinc bath to aid in shearing off excess zinc coat from galvanized metal parts.

Normally, the spent pickling acid from steel operations, containing only iron chloride as a major component, is disposed of by one of the following methods:

-   -   (a) neutralization, followed by water treatment and landfill of         solids;     -   (b) deep-well disposal; and     -   (c) recovery and recycling of excess HCI followed by recovery of         the following products from the spent HCI:         -   (i) FeCl_(2/3);         -   (ii) FeSO₄; and/or         -   (iii) FeO.

The larger steel mills and steel product processors mostly have implemented in-house neutralization units or recycling units making one of the three iron process by-products above. Also, because iron chloride is used in water treatment to soften water, steel manufacturers began selling spent pickling acid in as-is condition to water treatment facilities. Currently, sales of spent pickling acids, containing only iron chloride as the main component, into the water softening application constitutes the largest use of such spent pickling acids other than the operational in-house recycling units.

In the case of a spent hydrochloric acid from a galvanizing operation, the recovery and recycle of hydrochloric acid is more difficult because iron is mixed with zinc and a number of iron salts listed above cannot be made as pure components. Also, presence of Zn makes the spent acid unacceptable for direct water treatment applications. Although zinc is not a poison specifically, it is biologically active and may have unintended impact when used in an application having to do with human consumption.

There have been a number of attempts to separate ZnCl₂ and FeCl₂ using complexes followed by recycling of hydrochloric acid. However, the separation of Zn and Fe salts via complexes is expensive and normally is not justified by the costs of the separated salts. As a result, currently, only the deep-well disposal option is practical to handle spent pickling acid from a hot-dip galvanizing operation.

The most common recycling process used is the Ruthner process where water and HCl are flashed off and the iron chloride salts are further roasted in the presence of air to convert them into iron oxides. While simple enough, this process is energy-intensive as it requires evaporation of all of the possible volatiles and oxidation of iron chloride into iron oxide at 800° C. The materials requirements of such an operation are strenuous. See for example, “Metal Finishing Industry—Case Study 2”, 6 pages maintained on the worldwide web address cleanet.lk/noframes/case/metalB_case.htm discussing a number of methods to treat waste pickling acid, including the Ruthner process to achieve FeO and HCl for recycle, and making CaCl₂ for further inclusion in cement formulations.

There have been a number of efforts in the art to reduce the cost of recycling of pickling acid or to make valuable by-products more cost-effectively on a smaller scale for smaller steel mills and metal processing companies. For example, in 2000, two grants were issued by the U.S. Department of Energy to small companies to devise packaged processing systems to recycle hydrochloric acid and to make, in one case, ferrous sulfate FeSO₄, and in the other case, ferrous chloride, FeCl₂ by-products in an effort to make the recovery systems more affordable for smaller spent pickling acid generators. See, U.S. DOE Office of Industrial Technologies, “Steel Project Fact Sheet—Energy-Saving Regeneration of Hydrochloric Acid Pickling Liquor”, 2 pages, (2000); and U.S. DOE Office of Industrial Technologies, “Steel Success Story—Hydrochloric Acid Recovery System”, 4 pages, (2000). However, both of these technologies are not novel in their concept, the only novelty coming possibly from cheaper capital cost of a packaged recovery system realizing multiple sales from a one-time design and development cost. Furthermore, neither process is applicable for the galvanizing spent pickling acids because the iron salt by-products would not be sellable as they would contain zinc.

Prior Engineering (Switzerland) claims a proprietary process to separate zinc and iron chlorides by the use of extractants, but this process involves a number of steps and is expensive. See PRIOR Metal Technology, PEAG Technologie GmbH (Austria), “Solpex—Total Recycling—Processing of Waste Pickling Acids from Hot-Dip Galvanizing”, 2 pages contained on the worldwide website prioreng.com/site6_uk.htim.

Scientists at Poznan University of Technology (Poznan, Poland), developed a process to extract ZnCl₂ by using tributyl phosphate extractant. However, tributyl phosphate is an expensive material, and the losses of the expensive extractant make the extraction process not viable commercially. See, Sastre, Ana M. and J. Szymanowski, “Regeneration of Waste Hydrochloric Actid Solutions Containing Iron and Zinc Ions from Zinc Plating Plants.” NATO Science for Peace Programme, Project No. Sfp 972398, 2000-2003 found on the worldwide website of fct.put.poznan.pl/nato_sfp1.htm.

Hydrochloric acid is sometimes used as a leaching solution in processes to leach out Zn and Mg from mixed iron/Zn or iron/Mg ores. Iron is then displaced with an alkali metal like calcium (Ca) or sodium (Na) to precipitate out insoluble iron and zinc hydroxides forming a complex mixture of iron/zinc/chloride salts. However the iron/zinc chloride salts are not sellable as such a mixture, thus reducing the economic benefit of any application of this technology to the spent galvanizing pickling acid.

H.O. Hoffman, in Metallury of Zinc and Cadmium, briefly describes a process of neutralization of spent galvanizing pickling acid with lime, filtration, drying and calcining of the mixture of zinc and iron as paint. However, while in 1922, the material may have been suitable as paint pigment, the current pigment requirements make the product unsuitable as pigment because of large particle size and variability of color of the material within the same batch as well as from batch to batch. See, Hoffman, H.O, “Metallurgy of Zinc and Cadmium”, 1^(st) Ed., McGraw-Hill, N.Y., 1922.

Thus, spent hydrochloric pickling acid, especially that derived from a galvanizing process, is a waste product that is expensive to recycle or to convert into usable products, and a need exists to develop a process that could use it as an inexpensive raw material.

Meanwhile, a number of uses exist in a number of industries for a very stable, high density granular powder with a defined particle size. For example, the drilling industry requires a very high density, defined particle size powder to be used as a weighting agent in drilling muds. Drilling muds are very complex emulsions with a number of functions, such as a lubricant, carrier fluid for the drilling cuttings, drill well wall stabilizer, etc. Among these functions, the drilling muds have to be heavy to form a pressure seal on the well and to have adequate density to carry cuttings away. Normally, the weighing agents in the drilling muds are minerals barite (BaSO4) or hematite (Fe₂O₃). Typically, these minerals are mined and ground into appropriate size particles. The distinguishing characteristic of both minerals is that they are both very high density materials. For example, the specific gravity of barite is 4.33, while the specific gravity of hematite is 5.1. While the use of hematite would seem to be preferable due to its higher density, hematite, as opposed to barite, is very abrasive and wears out equipment, and, consequently, the use of barite is more widespread in the industry. The use of barite as a weighting agent for drilling muds is discussed generally in, e.g., U.S. Pat. No. 6,586,372 to Bradbury et al.

Thus a need still exists for a cost-effective, stable, high-density and low abrasiveness product that can be used as a drilling fluid weighting agent.

Additionally, there exists a need for a high stability dry powder with excellent absorption properties that can be used as a stabilizing material. Currently, high stability powders are used to stabilize hazardous aqueous and organic liquids prior to internment in a landfill. Stabilization of hazardous liquids means combining the liquid with an absorptive powder which absorbs the hazardous liquid components irreversibly and does not release the liquid once contained in a landfill. The absorbing powder usually used in stabilization now is lime kiln dust (LKD). LKD is a mixture of calcium oxide, calcium hydroxide and calcium carbonate powder that is collected in bag houses filtering the combustion air from lime kilns. Although LKD is commonly used because of its low price, its absorption capability is limited.

Thus, a need still exists for a cost-effective, high absorption capacity powder material able to stabilize hazardous wastes.

BRIEF SUMMARY OF THE INVENTION

To address the forgoing problems, a preferred embodiment of the present invention teaches a process of making a high density, high stability metal oxide mixture (and the product so produced) from waste spent pickling acid comprising the steps of. (a) providing a waste spent pickling acid having a desired ratio of metals; (b) reacting the pickling acid from step (a) to make a slurry consisting of solids comprising primarily metals and an aqueous liquid comprising primarily an alkali chloride; (c) filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate and a filter cake comprising primarily compounds of the metals; and (d) calcining the filter cake from step (c).

The waste spent pickling acid (or blends thereof preferably is waste spent galvanizing pickling acid containing predominantly iron and zinc metal in a desired ratio. A desired ratio of zinc to iron is less than or equal to about 0.75. Another desired ratio of zinc to iron is from about 0.5 to about 0.5854. More than one source of waste spent pickling acid can be provided, such as where a first source of spent pickling acid is provided having a ratio of zinc to iron from about 0 to about 1 and a second source of spent pickling acid is provided having a ratio of iron to zinc from about 0 to about 1. Where the pickling acids are blended, the blending step preferably takes place at temperatures ranging from about 40° F. to about 300° F.

The reacting step preferably comprises reacting the pickling acid from step (a) with alkali oxide, hydroxide or carbonate to make the slurry. The alkali oxide may preferably comprise one or a mixture from the group of sodium, calcium, potassium, lithium or magnesium. In a preferred embodiment, the reaction takes place at temperatures ranging from about 60° F. to about 400° F. In another preferred embodiment, the reaction takes place at temperatures designed to optimize the desired particle size of the solids. Ideally, the reaction pressures are sufficient to maintain in solution the volatile components of the waste pickling acid, and can range from about 0 psig to about 100 psig. Reaction residence time is preferably maintained to optimize the reaction slurry products and can range from about 0.1 hours to about 6 hours. In another preferred embodiment, the reaction residence time is maintained to optimize the pH of the reaction slurry product, preferably in the range of about 6.5 to about 8. The reacting step may take place in plug flow or stirred tank reactors, and the like, operated either in batch or in continuous mode, or in a series of continuous stirred reactors.

The filtration step uses filters known in the art, and is ideally conducted at temperatures in the range of about 60° F. to about 300° F. The filtration step may be optimized to prevent solids by-pass and enhance the clarity of the filtrate liquid, and in a preferred embodiment, the alkali chloride filtrate is substantially free of solids. Additionally, the filtration step can be optimized to increase filtration rates, such as, between about 0.06 gal/min/ft² and 0.5 gal/min/ft². The filtration step can also be optimized to permit filter cake accumulation rates of between about 4 lb/hr/ft² and 50 lb/hr/ft². Another preferred embodiment includes the additional step of washing the filter cake from step (c) at least once. Additionally, another preferred embodiment utilizes the step additional of washing, at least once, the filter cake product of step (d). The liquid alkali chloride filtrate of step (c) may be concentrated, such as, for example, by flashing. The pH of the concentrating step may preferably be adjusted to about 6.5 to about 8. The concentrated liquid alkali chloride filtrate may be filtered.

In a preferred embodiment, the calcining step oxidizes the filter cake to solids comprising a mixture of iron oxides, zinc oxides, alkali oxides, and/or various other partially hydrated oxides. In a preferred embodiment, the product of the calcining step comprises substantially oxides of zinc and iron. In another preferred embodiment, at least some of the iron and zinc oxides are present in the form of zinc ferrate. The temperatures employed in the calcining step preferably range from about 1100° F. to about 1500° F. In yet another embodiment, the temperatures employed in the calcining step are sufficient to drive off substantially all free water, absorbed water and chemically bound water, as well as remaining chlorides.

Yet another preferred embodiment includes the additional step of combining the filter cake solids separated in step (c) with an alkali material prior to the calcining step. Preferably, the alkali material is selected from the group of inexpensive industrial alkali materials, including, sodium hydroxide, sodium carbonate, calcium carbonate, calcium hydroxide, calcium oxide or by-pass streams, aqueous or dry, containing the above, including, lime kiln dust. The solids separated in step (c) are preferably combined with the alkali material in a weight ratio of solids to alkali adduct ranging from about 1:1 to 10:1 on a dry weight basis. Ideally, in one embodiment of the present invention, the absorbency of the solids separated in step (c) and subsequently calcined in step (d) is higher than 0.35 grams of water per gram of calcined product. In another preferred embodiment, the product of the calcining step comprises a powder of a particle size such that less than 15% of the particles are less than 6 micron equivalent diameter and do not pass through a 325 mesh screen) and 1.5% of the particles are greater than 75 micron equivalent diameter and do not pass through a 200 mesh screen. In still another preferred embodiment, the density of the calcined product is at least 4.5 and at most 5.5.

The processes of the present invention additionally provide a mechanism for producing a novel drilling fluid additive.

Another preferred embodiment of the present invention, there are provided novel products produced by the processes described herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a general block flow diagram of a process according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention is a process to manufacture high density, high stability, high absorption mixtures of metal oxides, preferably those comprising an iron oxide, zinc oxide and alkali metal oxide, and a high density, high stability, high absorption mixture of metal oxides, preferably comprising iron oxide, zinc oxide and alkali metal oxide from an inexpensive, and, preferably waste raw material such as galvanizing spent pickling acid. Galvanizing spent pickling acids normally contain excess hydrochloric acid, water, and salts of various metals, including such major components as iron chloride, zinc chloride, as well as various other contaminants most likely present as chlorides, such as lead, nickel, chromium, sodium, calcium, and some non-chloride oxides such as un-dissolved iron oxides, zinc oxides, and other oxides.

Referring now to FIG. 1, there is shown a flow diagram for a process 100 for making a high-density, high stability metal oxide mixture according to a preferred embodiment of the present invention. Two spent galvanizing pickling acid types, the high-iron 101 and the high-zinc 102 varieties are blended in a blending vessel 103 to give the desired ratio of iron to zinc in the blended spent galvanizing acid 104. The zinc/iron weight ratio can range from about 0 to about 1 in the type 101 spent pickling acid, and the iron/zinc ratio can range from about 1 to about 0 in the type 102 spent pickling acids. A desired weight ratio of zinc to iron in stream 104 is not more than about 0.75 and can be as low as 0, but preferably is in the range of about 0.1 to about 0.6 and even more preferably from about 0.5 to about 0.5854. Physically, blending can be accomplished in-line, in a stirred vessel or using any other effective mixing or blending method. Blending can be accomplished at ambient conditions, but preferably the blending should be accomplished at temperatures in the range about 40° F. to about 300° F., and more preferably about 60° F. to about 100° F.

When the desired composition of feedstock spent pickling acid is achieved, the spent pickling acid is reacted with an alkali metal oxide, hydroxide, or carbonate 105 in a reactor 106. The alkali metal in stream 105 may preferably be one or a mixture of sodium, calcium, potassium, lithium or magnesium. Reactor 106 may preferably be a plug flow or stirred tank reactor operated either in a batch or in a continuous mode. The reactor is preferably glass-lined. Also, a series of continuous stirred reactors may be used. Reaction temperature may be from about 60° F. to about 400° F., more preferably from about 150° F. to about 300° F., and more preferably from about 200° F. to about 250° F. As the alkali metal oxide, hydroxide or carbonate react with the iron, zinc and other heavy metal chlorides, insoluble precipitates of iron, zinc and other heavy metal oxides, hydroxides and partial oxides form. The temperature during precipitation is critical to the formation of appropriate size precipitate particles. Higher temperature, eg., 200° F. and above, aids in the formation of larger particle sizes. The reaction pressure should be sufficient to keep volatile components in the feedstock pickling acid in the liquid phase, normally in the range of about −14.7 psig to about 100 psig, more preferably in the range of about 0 psig to about 50 psig and yet more preferably in the range of about 0 to about 30 psig. The residence time in the reactor 106 may be from about 0.1 hours to about six hours, preferably from about 0.5 hours to about 4 hours and yet more preferably from about 0.5 hours to about 2 hours. The residence time in the reactor can be adjusted within the bounds of the preferred embodiment to achieve the pH of the reaction product from about pH 5 to about pH 8, preferably about pH 6.5 to about pH 7.5.

The crude reaction product comprising water, alkali metal chloride, and solids of iron and zinc oxide, hydroxide, chloride and partially oxygenated chlorides 107, is removed from the reactor 106 and filtered in filtration unit 108 to separate the solids 110 as a filter or centrifuge cake and the liquid aqueous alkali chloride stream 109. Filtration unit 108 may be a rotary drum or a rotary disk vacuum filter, a vacuum belt filter, a pressure leaf filter, a plate and frame filter, centrifuge or other suitable filtration device. However, due to the high solids loading, preferably, unit 108 is a continuous operation filter like a rotary drum or rotary disk filter. Filtration may be conducted at temperatures between about 60° F. and about 300° F., preferably in the range of about 150° F. to about 240° F., and more preferably in the range about 190° F. to about 220° F. In a preferred embodiment, the filtration unit 108 is a rotary drum or a belt filter with a knife discharge, and is operated to leave a thin layer (about ¼ to ⅛ inch) of filter cake on the cloth to prevent solids by-pass and enhance the clarity of the filtrate. Alternatively, filter cake may be blown off the filter cloth by air blow-back, exposing the filter cloth, which increases solids in the filtered product but also increases filtration rates. Filtrate rates of about 0.06 gal/min/ft² to about 0.3 gal/min/ft² and filter cake accumulation rates of about 4 lb/hr/ft² to about 50 lb/hr/ft² have been demonstrated when operating at the conditions of these preferred embodiments.

Optionally, in yet another representation of a preferred embodiment, the filtrate comprising alkali chloride 109 is collected, heated and flashed in unit 111 to remove excess water 112 from concentrated alkali chloride 113. Also in unit 111, the pH of the concentrated alkali chloride may be adjusted to about pH 6.5 to 8, preferably to about pH 7.5 to 8.0. The concentrated alkali chloride is then filtered in unit 114 to remove additional precipitated solids potentially including iron chloride, zinc chloride, iron oxide and other impurities. The finished liquid alkali product 115 is stored for sales.

In a preferred embodiment, filter cake 110 comprising iron, zinc, alkali metal and other trace metals, is calcined in the presence of air or oxygen in a calciner 116 at temperatures ranging from about 700° F. to about 1600° F., more preferably from about 1100° F. to about 1500° F. to drive off free water, absorbed water and chemically bound water as well as remaining chlorides, liberating them as hydrochloric acid and converting the salt into an oxide. Calciner 116 may preferably be a fluidized bed, a roaster, or a rotary calciner. The remaining solids may comprise a mixture of iron oxides, zinc oxide, alkali oxide and various other partially hydrated oxides. The solids 117 emerging from the calciner 116 are in a form of powder the particle size of which is controlled in the precipitation stage 106 as described above.

When the zinc to iron ratio of the feedstock spent galvanizing pickling acids is adjusted in unit 103 as described in a preferred embodiment of this invention, a large fraction of the iron and zinc oxides in stream 117 are present in the form of zinc ferrate, the mineral version of which is known as franklinite, a highly stable, high specific gravity mineral. Further, when the temperature is controlled during the precipitation stage 106 as described above, the particle size of the solid particle in stream 117 can be controlled.

In another preferred embodiment of the present invention, filter cake 110 is mixed with additional alkali oxide, hydroxide or carbonate prior to being fed into the calciner 116 in a ratio ranging from about 1:1 filter cake to alkali oxide, hydroxide or carbonate to about 10:1 filter cake to alkali oxide, hydroxide or carbonate on a dry weight basis. Alkali oxide will remain unchanged in the process of calcining. Alkali hydroxide and carbonate will be oxidized to an alkali oxide, thus amounting to an addition of alkali oxide to the predominantly iron and zinc oxide. Addition of alkali oxide to the mixture of iron and zinc oxide, although reducing density of the calcined solid, will enhance absorption capability and stability of the calcined powder for the use in applications as landfill stabilization material. In a preferred embodiment, the alkali oxide, hydroxide or carbonate used both in calciner 116 and in reactor 106 may be a commonly used, inexpensive industrial alkali material, including, inter alia, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, calcium carbonate, or by-product streams, aqueous or dry containing the above, including lime kiln dust, a common by-product from calcium processing.

In yet another embodiment of this invention, the filter cake 110 is washed in at least one stage, and possibly in as many as three stages, by water to reduce the content of alkali metal and chlorine prior to calcining in unit 116. Further, in this preferred embodiment, stream 117 is washed to remove additional amounts of alkali oxides. This treatment of stream 117 is useful for the applications that require high density characteristics. The resulting mixture will have a very high specific gravity ranging from about 4.5 to about 5.3 and is usable as a drilling fluid weighing component that is denser and therefore more cost-effective than barite or hematite. In a preferred embodiment, the calcined powder will be screened such that less than 15% of the particles is less than 6 micron equivalent diameter, 15% of the particles are greater than 45 micron diameter (does not pass through 325 mesh screen), and 1.5% of the particles are greater than 75 micron (does not pass through a 200 mesh screen). Those particles that are screened out as less than 6 micron or greater than 45 micron may be used for landfill stabilization application.

The calcined powder of stream 117 with low alkali content and high density is denser than barite, and has approximately the same density as hematite, but is less abrasive than hematite and is therefore superior in applications where the abrasiveness of hematite is problematic.

EXAMPLE 1

Spent galvanizing pickling solutions of types 101 (high iron) and 102 (high zinc) were mixed and analyzed for metals using procedure SW-846 6010B and for chlorine using method SW-4500-Cl-B (both procedures being known to those of ordinary skill in the art). This mixture (“Mixture 1”) was found to contain: TABLE 1 wt % Chloride 9.2 Iron 4.61 Zinc 2.59 Sodium 0.1617 Manganese 0.0369 Calcium 0.0196 Zinc/Iron 0.56

723 grams of Mixture 1 material was reacted with 90.4 grams of Ca(OH)₂ powder at room temperature to 7.16 final pH of the resulting slurry mixture. The resulting slurry was vacuum-filtered separating 433 grams of clear CaCl₂ brine and 323.3 grams of filter cake. The filter cake was washed with 393 grams of de-ionized water. After washing, a portion of the filter cake was dried at 125° C./257° F. overnight. The resulting powder was analyzed via XRD (X-ray diffraction) and found to contain 65% zinc ferrate (franklinite). The remaining 35% consisted of complex zinc and iron chlorates, perchlorates, and oxychlorides, partially hydrated.

EXAMPLE 2

Spent galvanizing pickling acid of type 102 (high zinc) (the same as in Example 1) was analyzed as described in Example 1 and was found to contain: TABLE 2 wt % Chloride 23.4 Iron 4.6 Zinc 15.8 Sodium 0.117 Manganese 0.0296 Calcium 0.0252 Iron/Zinc 0.29

The above acid was reacted with a Ca(OH)₂ slurry in water at ambient temperatures. The resulting slurry was filtered and the filter cake was washed and analyzed: TABLE 3 wt % Chlorine 4.75 Iron 6.34 Zinc 19.4 Sodium 0.0494 Manganese 0.0405 Calcium 2.25 Lead 0.0525 Nickel 0.0192 Chromium 0.0046 Aluminum 0.0331 Magnesium 0.0756

The filtrate was analyzed by density measurement to be a 21% CaCl₂ solution. This solution was placed in a boiling flask at atmospheric pressure and heated to 119° C./246° F. During the heating process a quantity of water was removed from the CaCl₂ solution via evaporation. The resulting concentrated calcium chloride was analyzed to be a 38% CaCl₂ solution.

EXAMPLE 3

6,326 grams of blended type 101 and type 102 spent pickling acid (“Mixture 2”) with initial pH of 0.1 was reacted with 3,725 grams of nominally 35% aqueous slurry of Ca(OH)₂ in a reactor padded with nitrogen. Addition of Ca(OH)₂ was continued until the pH of the resulting slurry reached 7.5.

The resulting slurry was filtered and separated into 7,003 grams of CaCl₂ and 4,044 grams of wet filter cake. The wet filter cake was washed with 1,000 grams of deionized water. 2,705 grams of washed filter cake was recovered. The washing process was repeated once.

The CaCl₂ filtered from the slurry was found to contain 15.2% CaCl₂ and was heated in a boiling flask to 119° C./246° F. to boil off excess water. The resulting calcium chloride was a 38% aqueous solution. Atomic Absorption (AA) analysis of product calcium chloride showed 62 ppm iron and 64 ppm Zn contaminants, well below industry-accepted specification levels.

1,009 grams of wet filter cake was calcined at temperatures from about 600° C. to 800° C. (about 1112° F. to 1472° F.) overnight. Specific gravity of the calcined powder was measured at 5.13.

EXAMPLE 4

12,824 grams of type 101 (high iron) spent galvanizing pickling acid was reacted with 5,212 grams of lime kiln dust over a two hour period. The temperature was allowed to vary, but was observed to be in the range of between about 25° C. and about 60° C. (77° F. and 140° F.). The final pH of the slurry after the two hour period was 7.11. The slurry was filtered. 822 grams of wet filter cake was dried at 125° C./257° F. overnight. The resulting weight of a dried cake was 384 grams. This material was calcined at 800° C./1472° F. The resulting weight of calcined powder was 312 grams.

50 grams each of lime kiln dust and the resulting calcined powder were separately measured and placed into separate containers and 5 cc of water was added to each and mixed in until a free water layer was noticed on top of each. Once the free water layer was observed, the wet mixtures were separately vacuum-filtered to remove free water. It was found that the calcined powder mixture retained 27 cc of water while the lime kiln dust retained 15 cc of water.

EXAMPLE 5

400 grams of the calcined powder from Example 4 was mixed with 110 grams of lime kiln dust and analyzed via a full TCLP method, including all SW 846 methods. All of the analyses except for those listed below show below detection limit. The following analyses (in parts per million) were above detection limits, but still below regulatory limits: TABLE 4 Component Regulatory limit Analysis Barium 100 1.47 Chromium 5 0.1

EXAMPLE 6

Specific gravities of several compounds used as drilling fluid weighing agents were found in the CRC Handbook of Chemistry and Physics, 73^(rd) Edition, 1992-1993, CRC Press, Inc., and compared to the specific gravity of zinc ferrate. TABLE 5 Fe₂O₃ Natural hematite 5.24 BaSO₄ Barite 4.5 ZnFe₂O₄ Zinc ferrate, Franklinite 5.33

The following represents an exemplary list of references.

U.S. PATENT REFERENCES

-   1. Elliott, U.S. Pat. No. 4,549,985, “Waste Disposal Process”, Oct.     29, 1985. 2. U.S. Pat. No. 6,395,242 Production of zinc oxide from     complex sulfide concentrates using chloride processing. -   3. Cornwell, U.S. Pat. No. 4,334,999, “Process for Extraction of     Metal Ions”, Jun. 15, 1982. -   4. Symens, et al., U.S. Pat. No. 6,730,234, “Method for Regeneration     of Used Halide Fluids”, May 4, 2004. -   5. laundon, et al., U.S. Pat. No. 4,940,572, “Process for Preparing     an Iron Oxide”, Jul. 10, 1990. -   6. Teyssier, et at, U.S. Pat. No. 4,299,809, “Process for the     Manufacture of Calcium Chloride”, Nov. 10, 1981. -   7. Douglas, et al., U.S. Pat. No. 4,298,581 “Process for recovering     chromium, vanadium, molybdenum and tungsten values from a feed     material”, Nov. 3, 1981. -   8. Bradbury, et al., U.S. Pat. No. 6,586,372 “Additive for     increasing the density of a fluid and fluid comprising such     additive”, Jul. 1, 2003.

OTHER REFERENCES

-   9. PRIOR Metal Technology, PEAG Technologie GmbH (Austria),     “Solpex—Total Recycling—Processing of Waste Pickling Acids from     Hot-Dip Galvanizing”, 2 pages. See worldwide website     prioreng.com/site6_uk.htim. -   10. U.S. DOE Office of Industrial Technologies, “Steel Project Fact     Sheet—Energy-Saving Regeneration of Hydrochloric Acid Pickling     Liquor”, 2 pages, 2000. -   11. U.S. DOE Office of Industrial Technologies, “Steel Success     Story—Hydrochloric Acid Recovery System”, 4 pages, 2000. -   12. Sastre, Ana M. and J. Szymanowski, “Regeneration of Waste     Hydrochloric Actid Solutions Containing Iron and Zinc Ions from Zinc     Plating Plants.” NATO Science for Peace Programme, Project No. Sfp     972398, 2000-2003. See the worldwide website of     fct.put.poznan.pl/nato_sfp1.htm. -   13. “Metal Finishing Industry—Case Study 2”, 6 pages. See worldwide     web address cleanet.lk/no frames/case/metalB_case.htm. -   14. Abstract of CEH report Hydrochloric Acid, Chemical Economics     Handbook, 2 pages, available on worldwide website ceh.sric.sri.com     Public/Reports/733.4000/ Abstract.html. -   15. Filippou, D, and Y, Choi, “A Contribution to the Study of Iron     Removal from Chloride Leach Solutions”, Abstract from Chloride     Metallurgy 2002: Practice and Theory of Chloride/Metal Interaction.     The Metallurgy Society of Canadian Institute of Mining, Metallurgy     and Petroleum (CIM). See also the worldwide website metsoc.org. -   16. Hoffman, H.O, “Metallurgy of Zinc and Cadmium”, 1^(st) Ed.,     McGraw-Hill, N.Y., 1922. -   17. World wide website of Cheney Lime & Cement Company (Allgood, AL)     “The Chemistry of Lime”, 3 pages, cheneylime.com/chemist.htm. -   18. “Calcium Chloride”, Encyclopedia of Chemical Technology,     Kirk-Othmer ed., 3^(rd) Ed., Vol. 4, pp. 801-811. -   19. “Electroplating”, Encyclopedia of Chemical Technology,     Kirk-Othmer ed., 3^(rd) Ed., Vol. 9, pp. 277-341. -   20. American Galvanizers Association list of member organizations     and businesses, 7 pages, 2003. See also their worldwide website     galvanizeit.org. -   21. Solubility Product, undated, 5 pages. -   22. Searls, James P, “Barite—2001”, U.S. Geological Survey Minerals     Yearbook—2001, pages 9.1-9.8 (2001). -   23. Searls, James P, “Barite”, U.S. Geological Survey, Minerals     Commodity Summaries, January 1998, pages 26-27. -   24. Birdsall, J. C., “An Overview of Hot Dip Zinc Galvanizing”, 7     pages, from “The Galvanizing Process” maintained on the worldwide     website of GTI Engineering, Inc. (Houston, Tex.) gtiengr.com -   25. “Calcium Chloride Feb. 1, 1999” —Chemical Market Reporter, Feb.     1, 1999. 2 pages from findarticles.com website. -   26. Reade Advanced Materials, “Hematite Powder from READE”, 3 pages,     from website of reade.com. -   27. M-I L.L.C. Product Bulletin “Hematite” 1996, 2 pages, available     on website e-federal.com. -   28. CRC Handbook of Chemistry and Physics, ₇₃ ^(rd) Edition,     1992-1993, CRC Press, Inc. -   All references referred to herein are incorporated herein by     reference. While the apparatus and methods of this invention have     been described in terms of preferred embodiments, it will be     apparent to those of skill in the art that variations may be applied     to the process and system described herein without departing from     the concept and scope of the invention. All such similar substitutes     and modifications apparent to those skilled in the art are deemed to     be within the scope and concept of the invention. Those skilled in     the art will recognize that the method and apparatus of the present     invention has many applications, and that the present invention is     not limited to the representative examples disclosed herein.     Moreover, the scope of the present invention covers conventionally     known variations and modifications to the system components     described herein, as would be known by those skilled in the art.     While the apparatus, compositions and methods of this invention have     been described in terms of preferred or illustrative embodiments, it     will be apparent to those of skill in the art that variations may be     applied to the process described herein without departing from the     concept and scope of the invention. All such similar substitutes and     modifications apparent to those skilled in the art are deemed to be     within the scope and concept of the invention as it is set out in     the following claims. 

1. A process of making a high density, high stability metal oxide mixture from waste spent pickling acid comprising the steps of: a. providing a waste spent pickling acid having a desired ratio of metals; b. reacting the pickling acid from step (a) to make a slurry consisting of solids comprising primarily metals and an aqueous liquid comprising primarily an alkali chloride; c. filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate and a filter cake comprising primarily compounds of the metals; and d. calcining the filter cake from step (c).
 2. The process of claim 1 wherein the waste spent pickling acid is waste spent galvanizing pickling acid.
 3. The process of claim 1 wherein the waste spent pickling acid contains predominantly iron and zinc metal in a desired ratio.
 4. The process of claim 3 wherein the desired ratio of zinc to iron is less than or equal to about 0.75.
 5. The process of claim 3 wherein the desired ratio of zinc to iron is from about 0.5 to about 0.5854.
 6. The process of claim 1 wherein more than one source of waste spent pickling acid is provided.
 7. The process of claim 6 wherein a first source of spent pickling acid is provided having a ratio of zinc to iron from about 0 to about 1 and a second source of spent pickling acid is provided having a ratio of iron to zinc from about 0 to about
 1. 8. The process of claim 7 wherein the first source of spent pickling acid comprises a blend of spent pickling acid from one or more sources.
 9. The process of claim 7 wherein the second source of spent pickling acid comprises a blend of spent pickling acid from one or more sources.
 10. The process of claim 7 comprising the additional step of blending the first and second sources of spent pickling acids prior to step (b).
 11. The process of claim 10 wherein the blending step results in a blended spent pickling acid having a desired ratio of zinc to iron.
 12. The process of claim 11 wherein the desired ratio of zinc to iron is less than or equal to about 0.75.
 13. The process of claim 10 wherein the blending step takes place at temperatures ranging from about 40° F. to about 300° F.
 14. The process of claim 1 wherein the reacting step comprises reacting the pickling acid from step (a) with alkali oxide, hydroxide or carbonate to make the slurry.
 15. The process of claim 14 wherein the alkali oxide comprises one or a mixture from the group of sodium, calcium, potassium, lithium or magnesium.
 16. The process of claim 14 wherein the reaction takes place at temperatures ranging from about 60° F. to about 400° F.
 17. The process of claim 1 wherein the reaction takes place at temperatures designed to optimize the desired particle size of the solids.
 18. The process of claim 14 wherein the reaction pressures are sufficient to maintain in solution the volatile components of the waste pickling acid.
 19. The process of claim 18 wherein the reaction pressures are in the range of about 0 psig to about 100 psig.
 20. The process of claim 14 wherein a reaction residence time is maintained to optimize the reaction slurry products.
 21. The process of claim 20 wherein the reaction residence time is from about 0.1 hours to about 6 hours.
 22. The process of claim 14 wherein a reaction residence time is maintained to optimize the pH of the reaction slurry product.
 23. The process of claim 14 wherein the pH of the reaction slurry product is in the range of about 6.5 to about
 8. 24. The process of claim 1 wherein the reacting step takes place in plug flow or stirred tank reactor operated either in batch or in continuous mode, or in a series of continuous stirred reactors.
 25. The process of claim 1 wherein the filtration step is conducted at temperatures in the range of about 60° F. to about 300° F.
 26. The process of claim 1 wherein the filtration step is optimized to prevent solids by-pass and enhance the clarity of the filtrate liquid.
 27. The process of claim 1 wherein the filtration step is optimized to increase filtration rates.
 28. The process of claim 1 wherein the filtration step is optimized to permit filtration rates of between about 0.06 gal/min/ft² and 0.5 gal/min/ft².
 29. The process of claim 1 wherein the filtration step is optimized to permit filter cake accumulation rates of between about 4 lb/hr/ft² and 50 lb /hr/ft².
 30. The process of claim 1 wherein the alkali chloride filtrate is substantially free of solids.
 31. The process of claim 1 further comprising the additional step of washing the filter cake from step (c) at least once.
 32. The process of claim 1 further comprising the step of washing, at least once, the product of step (d) comprising substantially oxides of iron and zinc.
 33. The process of claim 1 further comprising the additional step of concentrating the liquid alkali chloride filtrate of step (c).
 34. The process of claim 33 wherein the pH of the concentrating step is adjusted to about 6.5 to about
 8. 35. The process of claim 33 further comprising the additional step of filtering the concentrated liquid alkali chloride filtrate.
 36. The process of claim 1 wherein the calcining step oxidizes the filter cake to solids comprising a mixture of iron oxides, zinc oxides, alkali oxides, and/or various other partially hydrated oxides.
 37. The process of claim 1 wherein the temperatures employed in the calcining step range from about 1100° F. to about 1500° F.
 38. The process of claim 1 wherein the temperatures employed in the calcining step are sufficient to drive off substantially all free water, absorbed water and chemically bound water, as well as remaining chlorides.
 39. The process of claim 1 further comprising the additional step of combining the filter cake solids separated in step (c) with an alkali material prior to the calcining step.
 40. The process of claim 39 wherein the alkali material is selected from the group of inexpensive industrial alkali materials, including, sodium hydroxide, sodium carbonate, calcium carbonate, calcium hydroxide, calcium oxide or by-pass streams, aqueous or dry, containing the above, including, lime kiln dust.
 41. The process of claim 39 wherein the solids separated in step (c) are combined with the alkali material in a weight ratio of solids to alkali adduct ranging from about 1:1 to 10:1 on a dry weight basis.
 42. The process of claim 41 wherein the absorbency of the solids separated in step (c) and subsequently calcined in step (d) is higher than 0.35 grams of water per gram of calcined product.
 43. The process of claim 1 wherein the product of the calcining step comprises substantially oxides of zinc and iron.
 44. The process of claim 43 wherein at least some of the iron and zinc oxides are present in the form of zinc ferrate.
 45. The process of claim 1 wherein the product of the calcining step comprises a powder of a particle size such that less than 15% of the particles are less than 6 micron equivalent diameter and do not pass through a 325 mesh screen) and 1.5% of the particles are greater than 75 micron equivalent diameter and do not pass through a 200 mesh screen.
 46. The process of claim 43 wherein the density of the product is at least 4.5 and at most 5.5.
 47. A process of making a high density, high stability mixture of predominantly iron oxide, zinc oxide and zinc ferrate from waste spent galvanizing pickling acid comprising the steps of: a. providing a first source of waste spent galvanizing pickling acid having a ratio of zinc to iron from 0 to 1; b. providing a second source of waste spent galvanizing pickling acid having a ratio of iron to zinc from 0 to 1; c. blending the first and second sources of pickling acid to achieve a ratio of zinc to iron of about 0 to about 0.75. d. reacting the blended pickling acid from step (c) with alkali oxide, hydroxide or carbonate at temperatures and residence times to make a slurry consisting of optimum-sized solids comprising primarily iron and zinc and an aqueous liquid comprising primarily an alkali chloride; e. filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate that is substantially free of solids and a filter cake comprising primarily iron and zinc compounds; and f. calcining the filter cake from step (c) at temperatures to oxidize the iron and zinc compounds comprising the filter cake to a product comprising substantially oxides of iron and zinc.
 48. A process of making a drilling fluid additive comprising the steps of: a. providing a first source of waste spent galvanizing pickling acid having a ratio of zinc to iron from 0 to 1; b. providing a second source of waste spent galvanizing pickling acid having a ratio of iron to zinc from 0 to 1; c. blending the first and second sources of pickling acid to achieve a ratio of zinc to iron of about 0 to about 0.75. d. reacting the blended pickling acid from step (c) with alkali oxide, hydroxide or carbonate at temperatures and residence times to make a slurry consisting of optimum-sized solids comprising primarily iron and zinc and an aqueous liquid comprising primarily an alkali chloride; e. filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate that is substantially free of solids and a filter cake comprising primarily iron and zinc compounds; and f. calcining the filter cake from step (c) at temperatures to oxidize the iron and zinc compounds comprising the filter cake to a product comprising substantially oxides of iron and zinc.
 49. A high density, high stability metal oxide mixture manufactured by: a. providing a waste spent pickling acid having a desired ratio of metals; b. reacting the pickling acid from step (a) to make a slurry consisting of solids comprising primarily metals and an aqueous liquid comprising primarily an alkali chloride; c. filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate and a filter cake comprising primarily compounds of the metals; and d. calcining the filter cake from step (c).
 50. A high density, high stability mixture of predominantly iron oxide, zinc oxide and zinc ferrate made from waste spent galvanizing pickling acid by the process of: a. providing a first source of waste spent galvanizing pickling acid having a ratio of zinc to iron from 0 to 1; b. providing a second source of waste spent galvanizing pickling acid having a ratio of iron to zinc from 0 to 1; c. blending the first and second sources of pickling acid to achieve a ratio of zinc to iron of about 0 to about 0.75. d. reacting the blended pickling acid from step (c) with alkali oxide, hydroxide or carbonate at temperatures and residence times to make a slurry consisting of optimum-sized solids comprising primarily iron and zinc and an aqueous liquid comprising primarily an alkali chloride; e. filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate that is substantially free of solids and a filter cake comprising primarily iron and zinc compounds; and f. calcining the filter cake from step (c) at temperatures to oxidize the iron and zinc compounds comprising the filter cake to a product comprising substantially oxides of iron and zinc.
 51. A novel drilling fluid weighting agent of a high density, high stability mixture of predominantly iron oxide, zinc oxide and zinc ferrate made from waste spent galvanizing pickling acid by the process of: a. providing a first source of waste spent galvanizing pickling acid having a ratio of zinc to iron from 0 to 1; b. providing a second source of waste spent galvanizing pickling acid having a ratio of iron to zinc from 0 to 1; c. blending the first and second sources of pickling acid to achieve a ratio of zinc to iron of about 0 to about 0.75. d. reacting the blended pickling acid from step (c) with alkali oxide, hydroxide or carbonate at temperatures and residence times to make a slurry consisting of optimum-sized solids comprising primarily iron and zinc and an aqueous liquid comprising primarily an alkali chloride; e. filtering the slurry from step (b) to separate the aqueous alkali chloride from the solids thereby forming a liquid stream comprising alkali chloride filtrate that is substantially free of solids and a filter cake comprising primarily iron and zinc compounds; and f. calcining the filter cake from step (c) at temperatures to oxidize the iron and zinc compounds comprising the filter cake to a product comprising substantially oxides of iron and zinc. 